In rural areas septic tanks in conjunction with drain fields are utilized to handle and treat residential wastewater. Septic tanks typically comprise a concrete or plastic container that receives incoming waste water or influent from the sewage drains of the residence it serves. The septic tank incorporates biologically active agents to aerobically and anaerobically digest the waste constituents of the influent that enters the tank. The digestion process causes waste particles or solids once digested to precipitate to the floor of the septic tank and form a sediment referred to as sludge. On the surface of the waste water within the tank a layer of scum forms that includes a high grease content which is unable to be dissolved into the waste water. Biological agents in the scum layer digest the waste particles in this layer which causes these particles to precipitate to the sludge layer at the bottom of the tank. A so called clear zone separates the scum layer and the sludge layer in the tank. The so called clear zone is relatively clear of suspended solid waste particles but includes particles precipitating to the bottom of the tank as the density of the particles undergoes changes during digestion. Sludge gasification further causes bubbles to form in the sludge layer which when rising to the surface also carry particles with them.
Traditionally, relatively clear waste water is discharged as effluent from the clear zone of the tank into piping that carries the effluent to a drain field or leach field. The drain field typically comprises a highly porous bed of gravel, sand or other coarse and fine aggregates. The drain field is usually disposed underground below the level of the septic tank but at a depth above the groundwater level. The drain field is efficient in allowing the wastewater to leach or percolate into the ground and eventually into the groundwater. Water leaching through the porous drain field is further filtered of solids by the gravel and sand of the drain field. Additionally, aerobic and anaerobic digestion of solids occurs in the drain field. By the time the wastewater has reached the groundwater supply it has been treated by the digestion process within the septic tank and from the filtering effect of the drain field.
The quality of wastewater that is permitted to enter the groundwater supply is stringently regulated in some areas to minimize the negative environmental effects that are associated with poorly treated wastewater entering the groundwater supply. These regulations have necessitated improvements to the traditional septic tank and drain field residential waste water handling system. Furthermore, as solid waste particles are discharged unintentionally from the septic tank to the drain field, the porous structure of the drain field has a tendency to become clogged with these solids thus diminishing the drainage capabilities of the drain field. Improvements have been incorporated into the traditional septic tank and drain field design to minimize the amount of solids that are discharged into a drain field to thus insure a maximum drainage efficiency.
The two goals of maximum drain field drainage efficiency and minimum environmental impact have been best achieved in the past by the incorporation of a filter device placed in the septic tank to filter effluent leaving the tank. This filter, once utilized, insures that a minimum of untreated solid waste particles are discharged from the tank into the drain field. Additionally, maximum drain field drainage efficiency has been further advanced by the use of an incremental discharge apparatus such as a dosing siphon or pump to discharge the effluent from the tank to the drain fields. The use of an incremental discharge apparatus further necessitated the use of a filter to minimize the clogging effects of solids on the devices. Incremental discharge apparatus provide the benefit of discharging a large volume of water from the tank at spaced time increments. This type of discharge has a cleansing effect on solids accumulating within piping and within the drain field, as well.
These previous attempts at filtering the effluent that is discharged from a septic tank into a drain field have been successful in limiting the amount of untreated solid waste particles exiting the septic tank. Nevertheless, previous effluent filters had inherent inefficiencies due to their construction. Previous effluent filters are typically of a first design that utilizes a single filtering surface that is mounted in a housing, or of a second design that utilizes a filter comprising multiple stacked filtering elements within a housing. The first filter design which incorporates a single filter surface typically further incorporates a pump or other discharge apparatus that is maintained within the interior of the filter to permit the incremental discharge of filtered waste water to the drain field.
A first deficiency of both previous types of effluent filters is the clogging effect of suspended particles caused by the flow patterns within the filter and housing. In either system, waste water that enters the housing passes through the single filter surface or through one of the multiple stacked filter elements in essentially unidirectional flow. This unidirectional flow causes solid waste particles to accumulate on the filter surface or within the filter elements so as to progressively minimize the efficiency of the filter until it is completely clogged.
A second deficiency in the two previous filter designs is the lack of self cleaning properties. Solid waste particles that enter the housing are subject to digestion but are unlikely to be removed from the housing due to the unidirectional flow patterns within the housing.
A third deficiency of the two previous filter designs is a result of the manner that waste water is supplied to the filter. In either design there is essentially a single route or flow pattern for waste water to proceed into the housing and through the filter. In the past filter designs utilizing a single filter surface, waste water is able to enter the housing at various openings all of which advance the waste water to the same location within the housing and provide the waste water with a single surface such as a screen through which the waste water must pass to be discharged from the tank by a suitable means. Similarly, in the past filter designs utilizing multiple stacked filter elements, waste water enters the housing only at a single location and is then able to proceed through the filter. If the filter surface or filter elements of either system clog, no alternative flow pattern is possible to pass water through the filter. Furthermore, if the single location opening of the housing become clogged by the eventual upward advancement of the sludge layer or by the eventual downward movement of the scum layer the housing will not provide an alternative flow pattern for the waste water to access the filter.
A fourth deficiency in the first and second previous effluent designs has been the inability to back flush the filter. This feature is a necessity considering the inherent tendency of the previous filter designs to clog with solid particles quite easily.
In lieu of the deficiencies of previous effluent filter designs there is clearly a need for a filter that: minimizes the clogging effects of accumulating solid waste particles on the filter surface by providing an alternative to unidirectional flow through the filter; provides self cleaning to the filter so as to minimize costly maintenance; provides alternative flow patterns through the filter to maximize efficiency and to provide the filter the capability to function if a single flow pattern is not functioning; and can be easily back flushed.